I'm installing Ubuntu server on a disk with 12GB available. During the setup, I choose the default LVM-based partition layout.

However for some reason, Ubuntu decides that it only wants to use 4GB of this disk. How do I reclaim the remaining space of the hard disk? "lvextent" doesn't work btw...

output of df -h:

Filesystem               Size  Used Avail Use% Mounted on
/dev/mapper/ubuntu-root  4.3G  3.4G  754M  82% /
udev                     3.9G  4.0K  3.9G   1% /dev
tmpfs                    1.6G  756K  1.6G   1% /run
none                     5.0M     0  5.0M   0% /run/lock
none                     3.9G     0  3.9G   0% /run/shm
/dev/sda1                228M   25M  192M  12% /boot

output of pvdisplay:

  --- Physical volume ---
  PV Name               /dev/sda5
  VG Name               ubuntu
  PV Size               12.32 GiB / not usable 2.00 MiB
  Allocatable           yes 
  PE Size               4.00 MiB
  Total PE              3154
  Free PE               8
  Allocated PE          3146
  PV UUID               dD06RZ-kGcL-1tTX-Ruds-XIDG-ssMd-FIUkzZ

my partitions:

Device       Boot         Start         End              Blocks        Id   System
/dev/sda1     *            2048      499711             248832         83   Linux
/dev/sda2                501758    26343423           12920833          5   Extended
/dev/sda5                501760    26343423           12920832         8e   Linux LVM

when I try lvextent, it says there is not enough diskspace.